In manufacturing it is often necessary to locate fixture plates (holding fixtures) on the table of a machine tool or on a base plate attached to the table of the tool used to perform an operation. In general, a variety of machine tools, such as lathes, milling machines, routers, etc. may be used in manufacturing. Each time a holding fixture is positioned on a machine table or base plate, it must be accurately located with respect to the axes of the machine and firmly secured. The usual procedure is to locate the fixture with a minimum of two dowels which are passed through holes in the fixture plate into corresponding holes in the machine table or base plate attached to the table below. Similarly, cap screws are used to secure the fixture to the table. Screws pass through the fixture into corresponding threaded holes in the base plate or machine table below. Each time a holding fixture is mounted on a machine tool, the appropriate sizes and quantities of screws and dowels must be located and inserted into the correct holes. This involves a significant amount of time, particularly if the required hardware is misplaced or lost.
The prior art addresses some of these problems by use of locating bushings in the fixture plate, corresponding receiver bushings in the machine tool table or a base plate attached to the machine, and a locator containing a mechanism which forces several balls radially outwardly into an annular groove in the receiver bushing. The shank of the locator projects a considerable height above the working surface of the fixture plate. This limits the space available for positioning the work piece on the holding fixture and creates the possibility of cutter path interference. In addition, another drawback of this design is its complexity, which adds considerably to its cost.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved screw assembly for temporarily affixing a component, such as a fixture plate, on the base plate of a tool or the like.
Another object of the invention is to provide a new and improved screw assembly with captured components so that searching for components is eliminated.
Another object of the invention is to provide a new and improved screw assembly that is relatively inexpensive and easy to fabricate.